Some embodiments relate to devices for generating a polychromatic beam of photons, and to analyzing systems that use such devices.
As those of ordinary skill in the art know, in certain fields, such as for example that of the analysis of samples (possibly medical samples), spatially coherent polychromatic laser sources are required. Such sources are frequently called continua because they deliver a beam of photons having wavelengths that are substantially continuously distributed over a large spectral width, typically a few tens of nanometers to a few hundred nanometers.
These sources are produced on the basis of a light-matter interaction employing non-linear effects. They generally include at least one continuous-wave or pulsed laser source (see [R1]) that delivers “primary” photons having a “primary” wavelength, and a microstructured optical fiber or non-linear crystal that is arranged to produce, from the primary photons, an output beam including secondary photons having a plurality of “secondary” wavelengths.
Sources employing a micro-structured optical fiber allow stable emissions with a spectral width extending from the near ultraviolet (or UV) (about 350 nm) to the mid infrared (typically 5 μm) to be obtained. Micro-structured optical fibers made of silica are for example limited in the infrared to 2.4 μm, and have the particularity of confining the luminous power, thereby increasing the light-matter interaction and improving the conversion of the primary wavelength to a large number of secondary wavelengths. However, non-linear micro-structured optical fibers have a small core diameter and therefore, in the presence of a high confinement of energy, the threshold for damage of their material is very quickly reached. Thus, these sources employing a micro-structured optical fiber do not allow high output energies to be obtained. In addition, they do not allow wavelengths belonging to the entire UV domain (shorter than 340 nm) and the entire infrared domain to be obtained simultaneously. Lastly, they do not allow the group velocities of secondary photons of different wavelengths to be equalized, this inducing a desynchronization of secondary photons of different wavelengths over time. As a result, it is impossible to use these sources in certain applications, such as for example multiplex coherent anti-Stokes Raman scattering (CARS), which is in particular used in the field of imaging to identify and locate specific chemical species within a sample.